Methods for cross color and/or cross luminance suppression

ABSTRACT

A method for processing an image in a video data is provided. The video data has a plurality of frames. The method includes: obtaining a plurality of differences, each difference in the plurality of differences being obtained from two frames that are one frame apart, wherein the each difference in the plurality of differences is between pixel information of one pixel from a plurality of pixels in one of the two frames, and a corresponding pixel in the other frame of the two frames; examining a first criterion with a summation of the plurality of differences; and performing cross color suppressing operation on a current frame of the plurality of frames according to a set of stationary image judgment information comprising the result of the first criterion examination.

CROSS REFERENCE TO RELATED APPLICATIONS

This continuation application claims the benefit of co-pending U.S.patent application Ser. No. 10/710,072, filed on Jun. 16, 2004 (now U.S.Pat. No. 7,280,159) and incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods for improving display qualityof an image. More specifically, the present invention is directed tomethods of performing cross color and/or cross luminance suppression toimprove display quality.

2. Description of the Prior Art

In composite video television systems such as NTSC and PAL, a luminancesignal and a chrominance signal share a portion of the availablebandwidth. In NTSC, for example, chrominance information is encodedthrough a sub-carrier having frequency equaling 3.57955 MHz. Within thechrominance band extending from roughly 2.3 MHz to 4.2 MHz, theluminance spectrum overlaps that chrominance spectrum. This overlapresults in signal interference.

It is well-known that a television decoder is implemented to extractboth luminance information and chrominance information from the receivedcomposite signal; however, a typical simple television decoder cannotdiscern which of the higher frequency components are luminanceinformation and which are chrominance information. As a result, such atelevision decoder generates incorrect chrominance information owing tothe interference introduced via the luminance spectrum. The term “crosscolor” is commonly referred to as corruption of the chrominance spectrumcaused by the misinterpretation of high-frequency luminance informationas wanted chrominance information. Conversely, the term “crossluminance” is commonly referred to as corruption of the luminancespectrum caused by the misinterpretation of chrominance information ashigh-frequency luminance information.

Some conventional methods reduce cross color by operating uponchrominance information encoded on the chrominance subcarrier prior todemodulation into baseband chrominance information. These methodstypically incorporate cross color suppression into the decoding process,focusing on improving the separation of the chrominance and luminanceinformation to reduce both cross color and cross luminance.

However, cross color suppression is very desirable in applications whereonly demodulated baseband chrominance information is available,especially where demodulation was performed without much regard forsuppressing cross color. In such applications, for practical reasons,cross color suppression must be performed in the baseband domain.

As such, Faroudja describes a technique for suppressing cross color inU.S. Pat. No. 5,305,120, the contents of which are hereby incorporatedby reference. Although Faroudja suggests a feasible approach forpost-decoding cross color suppression, a more optimized motion detectionalgorithm is desired in order to minimize possible error occurrence inthe outcome of cross color suppression caused by over-simplifiedstationary image judgment.

SUMMARY OF THE INVENTION

It is therefore one of the objectives of the claimed invention toprovide methods of suppressing cross color and/or cross luminance of animage by introducing a well-designed motion detection algorithm.

According to one exemplary embodiment of the present invention, a methodfor processing an image in a video data is provided. The video datacomprises a plurality of frames. The method comprises: obtaining aplurality of differences, each difference in the plurality ofdifferences being obtained from two frames that are one frame apart,wherein the each difference in the plurality of differences is betweenpixel information of one pixel from a plurality of pixels in one of thetwo frames, and a corresponding pixel in the other frame of the twoframes; examining a first criterion with a summation of the plurality ofdifferences; and performing cross color suppressing operation on acurrent frame of the plurality of frames according to a set ofstationary image judgment information comprising the result of the firstcriterion examination.

According to another exemplary embodiment of the present invention, amethod for processing an image in a video data is provided. The videodata comprises a plurality of frames. The method comprises: obtaining afirst difference set between pixel information of one of the frames andpixel information of another one of the frames, wherein the two framesinvolving the first difference set are one frame apart, and the firstdifference set comprises a plurality of differences, each difference ofthe plurality of differences being between pixel information of a pixelin one of the two frames involving the first difference set and pixelinformation of a corresponding pixel in the other one of the two framesinvolving the first difference set; summing the absolute values of eachdifference in the plurality of differences of the first difference setto thereby obtain a sum of absolute differences; examining a firstcriterion according to the sum of absolute differences; and performingcross color suppressing operation on pixel information of a currentframe of the plurality of frames according to a set of stationary imagejudgment information comprising the result of the first criterionexamination.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a cross color and cross luminancesuppression apparatus according to an embodiment of the presentinvention.

FIG. 2 is a timing diagram conceptually illustrating a plurality ofsequentially incoming image frames of the apparatus in FIG. 1.

FIG. 3 is a diagram illustrating the pixel allocation of a portion ofthe image frames in FIG. 2.

FIG. 4 is a timing diagram conceptually illustrating a plurality ofsequentially incoming image fields of the apparatus in FIG. 1, embodiedby the portion shown in FIG. 3 of a plurality of image frames in FIG. 2.

FIG. 5 is a flowchart illustrating the method of cross color and/orcross luminance suppression according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

Please refer to FIG. 1, which is a block diagram illustrating a crosscolor and cross luminance suppression apparatus 100 according to anembodiment of the present invention. In this embodiment, the apparatus100 comprises a motion detector 102 and a processor 104. The motiondetector 102 successively receives a plurality of pixel information,which may include, in one embodiment, luminance information (Y) andchrominance information (U and V, or C.sub.r and C.sub.b),representative of a series of pixel data in image frames. The motiondetector 102 then generates a motion control signal according to thereceived pixel information. The motion control signal indicates whethera current pixel is deemed stationary (i.e., still), or deemed to be withmotion. The processor 104 also receives the pixel information, here, theluminance information and the chrominance information, and performscross color suppressing operation on the chrominance information, aswell as cross luminance suppressing operation on the luminanceinformation. By doing so, the pixel information output by the processor104 is substantially free of cross color and cross luminance influence.

Before further explaining the operation of apparatus 100, certainpreliminary knowledge pertaining image frame composition should beunderstood. Here, the well-known NTSC systems are hereby taken as anexample for explanatory purpose. Please refer to FIG. 2, which is atiming diagram conceptually illustrating a plurality of sequentiallyincoming image frames of the apparatus 100. As is well-known in the art,in NTSC systems pixel data are sequentially transmitted and processed ina separate even field and odd field fashion, as illustrated in FIG. 4,while pixel data in the even field and in the odd field are interlacedto constitute a full image frame, as illustrated in FIG. 3. In FIG. 2,FIG. 3, and FIG. 4, four image frames 3, 2, 1, 0 are sequentiallyarranged at time T-3, T-2, T-1, and T in a timely fashion. It is to benoted that in FIG. 3 and FIG. 4 only a portion of an image frame (9pixels in each field, or 18 pixels in each frame) is illustrated forsimplicity, wherein the notations A, B, C, D, E, F, G, H, and I arerepresentative of pixel data at respective location of a field, thesubstripts “e” and “o” correspond to the even field and the odd field,respectively, and the superscripts correspond to frame numbers.

As is well known to one of ordinary skill in the art, in NTSC systems,which are adopted as an example in the following description of theembodiment of the invention, the chrominance subcarrier phase rotates by180 degrees between successive frames. This rotation causes luminanceinformation to be misinterpreted as chrominance information, whichoscillates between two complementary colors such as red and green; thatis, the luminance appears to be spectral energy which oscillates betweentwo colors represented by chrominance information 180 degrees out ofphase with each other. Similar 180-degree phase rotation betweensuccessive frames can also be observed when examining the crossluminance phenomenon, i.e., the corruption of the luminance spectrum bythe chrominance information.

Therefore, by averaging the chrominance information in two successiveframes the out-of-phase cross color information cancels thereby allowingchrominance information to be obtained which is substantially free ofcross color. Likewise, the cross luminance information can also becancelled by similar averaging operation. However, this technique worksmost effective when the image is stationary, or still. As a result, awell-designed motion detection algorithm (or a stationary judgmentalgorithm) may serve to enhance the cross color suppression and/or crossluminance suppression effect, as well as the resultant display qualityof the outcome of the processing, since improper cross color and/orcross luminance suppressing operation based on a poor motion detectionalgorithm degrades the display quality drastically.

As such, in an embodiment of the present invention, a motion detectionalgorithm adopted by the motion detector 102 is to be provided as in thefollowing descriptions. Take the sequentially incoming image fieldsshown in FIG. 4 as an example, for each of the incoming pixel data (forexample, the pixel Eo as a current pixel), the motion detector 102checks for a number of conditions. As a first condition, the motiondetector 102 checks for the similarity between the current frame 0 attime T and the previous frame 2 at time T-2, which is two frames priorto the current frame 0, for they are of the same phase in crosscolor/cross luminance phenomena. This condition may be implemented byobserving the values of the following functions:dY ₁ =|Y _(Eo) −Y″ _(Eo)|<Thl_(—) Y ₁  (1)dU ₁ =|U _(Eo) −U″ _(Eo)|<Thl_(—) U ₁  (2)dV ₁ =|V _(Eo) −V″ _(Eo)|<Thl_(—) V ₁  (3)

wherein Y, U, and V represent the one luminance information and twochrominance information of the corresponding pixel data, respectively,and Thl_Y, Thl_U, and Thl_V are threshold values, whose amounts shouldbe determined according to actual applications. In this embodiment, onlywhen the values of the above three functions (1), (2), and (3) are alltrue, is the first condition asserted to be true.

Please note that, although in this embodiment differences in pixel databetween two frames are adopted to indicate the degree of similaritybetween two frames, other known way of indicating similarity may also beutilized. Please also note that, although in this embodiment only thepixel information of the current pixel (i.e., Eo) is adopted forsimilarity determination, more pixels may be incorporated into suchdetermination. For example, the function of (1) may also be substitutedby the following function:

$\begin{matrix}{{dY}_{1} = {{\sum\limits_{X = {{Ao} \sim {Io}}}{{Y_{X} - Y_{X}^{''}}}} < {Thl\_ Y}_{1}}} & (1)^{\prime}\end{matrix}$

That is, in addition to the current pixel Eo, the surrounding eightpixels in the same field are also incorporated into the similaritydetermination. Of course, the number and position of pixels incorporatedmay be altered, and similar substitutions may also be asserted tofunctions (2) and/or (3).

Moreover, in determining whether the image is stationary or not for thecurrent pixel, here, Eo, it may also be instructive to check for thesimilarity between a corresponding pixel (Ee) in the complementaryfield, here, the even field, of the same frame, and a pixel (Ee″) twoframes prior thereto. This is because pixels in the complementary fieldof the same frame contributes half of the frame, and therefore should beindicative in determining if an image being stationary or not. Likewise,the above-mentioned adoption of Y, U, and/or V pixel information indetermining similarity, and the adoption of multiple pixels around thecurrent pixel, may also be applied to such checking for similaritybetween the complememtary field and its predecessor two frames ahead.

When deriving a result for the first condition, it may also bemeaningful to optionally check for the similarity between the precedingframe 1 at time T-1 of the current frame 0, and the frame 3 at time T-3,which is two frames prior to the frame 1. As an example, the followingthree functions can be utilized:dY ₂ =|Y′ _(Eo) −Y′″ _(Eo)|<Thl_(—) Y ₂  (4)dU ₂ =|U′ _(Eo) −U′″ _(Eo)|<Thl_(—) U ₂  (5)dV ₂ =|V′ _(Eo) −V′″ _(Eo)|<Thl_(—) V ₂  (6)

This is because in determining whether an image at time T is stationaryor not, it might also be indicative to check if the image one frameahead (i.e., at time T-1) is also stationary, for stillness of an imageis construed in a consecutive context. In an embodiment where thesefunctions are incorporated in determining the outcome of the firstcondition, only when the values of the functions (1), (2), (3), (4),(5), and (6) are all true, is the first condition asserted to be true.

Of course as can be appreciated by those of ordinary skill in the art,the above-mentioned adoption of multiple pixels around the currentpixel, and the adoption of pixel information of the complementary fieldsmay also be applied to such checking for stillness between the frame 1and its predecessor frame 3, which is two frames ahead.

In addition to the first condition, a second condition, wherein thesimilarity between a frame that is one frame ahead of the current frame(i.e., the frame 1 at time T-1 ), and an adjacent frame thereof (forexample, the frame 2 at time T-2), is further considered in determiningthe stillness of the image for the current pixel. The checking forsimilarity between two adjacent frames, though may not as significantdue to the 180 degree out-of-phase characteristic in cross color of theNTSC systems, can still be of meaning in determining stillness,considering the consecutive nature of the stillness in image. In thisembodiment, the second condition may be implemented by observing thevalues of the following functions:dY ₃ |Y′ _(Eo) −Y″ _(Eo)|<Thl_(—) Y ₃  (7)dU ₃ =U′ _(Eo) −U″ _(Eo)|<Thl_(—) U ₃  (8)dV ₃ =V′ _(Eo) −V″ _(Eo)|<Thl_(—) V ₃  (9)

Similarly in this embodiment, only when the values of the above threefunctions (7), (8), and (9) are all true, is the second conditionasserted to be true.

In addition to the three functions (7), (8), and (9), furtherobservations can be incorporated in determining the outcome of thesecond condition, such as the similarity between the frame which is twoframes ahead of the current frame (i.e., the frame 2 at time T-2) and anadjacent frame thereof (for example, the frame 3 at time T-3). Thefollowing functions may serve as one such example:dY ₄ =|Y″ _(Eo) −Y′″ _(Eo)|<Thl_(—) Y ₄  (10)dU ₄ =|U″ _(Eo) −U′″ _(Eo)|<Thl_(—) U ₄  (11)dV ₄ =|V″ _(Eo) −V′″ _(Eo)|<Thl_(—) V ₄  (12)

And in such an embodiment, only when the values of the functions (7),(8), (9), (10), (11), and (12) are all true, is the second conditionasserted to be true.

Please note that, when the required pixel information is available, theabove-mentioned functions (7), (8), (9) may also be adapted to check thesimilarity between the frame 1 and the other adjacent frame thereof,which is the current frame 0, and the above-mentioned function (10),(11), (12) may also be adapted to check the similarity between the frame2 and the other adjacent frame thereof, which is the frame 1. Also ascan be appreciated by those of ordinary skill in the art, theabove-mentioned adoption of multiple pixels around the current pixel,and the adoption of pixel information of the complementary fields mayalso be applied to such checking for similarity between two adjacentframes.

In addition to the first and the second conditions, a third condition,which is termed as the “high-frequency stillness” condition, is furtherexamined in determining the stillness of the image for the currentpixel. The third condition checks for the consecutive stationarysituation of frames 0, 1, and 2 respectively at time T, T-1, and T-2 byutilizing, as an example, the following operations. First, the followingoperators are so defined:dNext_(—) Y=Y′ _(Eo) −Y″ _(Eo)dPre_(—) Y=Y′ _(Eo) −Y″ _(Eo)dNext_(—) U=U′ _(Eo) −U _(Eo)dPre_(—) U=U′ _(Eo) −U″ _(Eo)dNext_(—) V=V′ _(Eo) −V″ _(Eo)dPre_(—) V=V′ _(Eo) −V″ _(Eo)

Then, the following condition pertaining the operator dNext_Y is checkedto find out the value of an additional operator Next_Y:

if (dNext_Y > Thl_Y₅) Next_Y = 1(True) elseif (dNext_Y < −Thl_Y₅) Next_Y= −1(True) else Next_Y = 0(False)

Similar conditions respectively pertaining the operators dPre_Y,dNext_U, dPre_U, dNext_V, and dPre_V are also checked to find outcorresponding operators Pre_Y, Next_U, Pre_U, Next_V, and Pre_V. Andlastly, the following condition pertaining the operators Next_Y andPre_Y is further checked to find out the value of yet another operatorNextPre_Y:

if (Next_Y > 0 & & Pre_Y > 0) NextPre_Y = 1(True) elseif (Next_Y < 0 & &Pre_Y < 0) NextPre_Y = 1(True) else NextPre_Y = 0(False)

Similar conditions respectively pertaining to the operators Next_U andPre_U, Next_V and Pre_V, are also checked to find out correspondingoperators NextPre_U, and NextPre_V. Here if the value of the operatorNextPre_Y is true, high-frequency alternation in Y domain is deemedexisting, and high-frequency alternation phenomenon is not desirable foran image regarded as stationary. Therefore, in this embodiment, onlywhen the values of the operators NextPre_Y, NextPre_U, and NextPre_V areall false, is the third condition asserted to be true. Please note that,to a person of ordinary skill in the art, it is understood that such ahigh-frequency stillness condition may also be expanded to incorporatelaterally adjacent pixels (Do and/or Fo) and/or vertically adjacentpixels (Bo and/or Ho) of the current pixel Eo.

After all these operations are performed, the motion detector 102determines whether the image is stationary or not for the current pixel.In this embodiment, the image is deemed stationary for the current pixelonly when the first, the second, and the third conditions are allasserted to be true.

Please note that the hardware requirement, particularly the memoryrequirement, of the motion detector 102 to perform the above-mentionedcondition check varies according to the complexity of conditionsactually adopted, from 8 field buffers to 4 field buffers, as will beappreciated by those of ordinary skill in the art. Also note that here,the estimated field buffer requirement need not include currentlyincoming image field, taking the advantage of a pixel-by-pixeloperation.

After the motion detector 102 decides whether the image is stationary ornot for the current pixel, the motion control signal is then passed tothe processor 104 to inform the processor 104 of the determination ofthe motion detector 102. If the image is deemed stationary for thecurrent pixel, the cross color suppression and/or the cross luminancesuppression operation is launched by, in this embodiment, averaging thepixel information across two consecutive image frames (for example,(Y_(Eo)+Y_(Eo)′)/2, (U_(Eo)+U_(Eo)′)/2, and (V_(Eo)+V_(Eo)′)/2), orother suppression methods known to a skilled artisan. If the image isdeemed not stationary (i.e., with motion), in this embodiment thecurrent pixel is output as received.

Please refer to FIG. 5, which is a flowchart illustrating theaforementioned condition checks and cross color and/or cross luminancesuppression operation according to an embodiment of the presentinvention. A person of ordinary skill in the art should be able tounderstand that the order of performing the checking steps 502, 504, and506 in FIG. 5 serves only as an example, is not meant to be limiting,and may be changed. Also note that when any of the first, the second,and the third condition is not met, pixel data are outputted as receivedin step 510 in this embodiment, further processing on the pixel dataoutputted may also be done in other embodiments.

Although the detailed description of the embodiments of the inventionhas been focused on the application in NTSC systems, the presentinvention may also be adapted to other display systems, such as the PALsystems. One point worth noting is that for PAL systems, the chrominancesubcarrier phase rotates by 90 degrees between successive frames, as isthe case for the luminance subcarrier. Therefore, the misinterpretationof luminance information as chrominance information rotates in phase by90 degrees for each incoming frame. With this in mind, a skilled artisanshould be able to substitute the claimed invention into a PAL system,and gain from similar improved display quality.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A method for processing an image in a video data, the video datacomprising a plurality of frames, the method comprising: obtaining aplurality of differences, each difference in the plurality ofdifferences being obtained from two frames that are one frame apart,wherein each difference in the plurality of differences is between pixelinformation of one pixel from a plurality of pixels in one of the twoframes, and a corresponding pixel in the other frame of the two frames;examining a first criterion with a summation of the plurality ofdifferences; and performing cross color suppressing operation on acurrent frame of the plurality of frames according to a set ofstationary image judgment information comprising a result of the firstcriterion examination.
 2. The method of claim 1 further comprising:obtaining a first difference set including at least a difference fromthe plurality of differences, and examining the first criterion with thefirst difference set.
 3. The method of claim 2, wherein each differencein the first difference set further indicates differences between pixelinformation of one of a plurality of pixels in a vicinity of a targetpixel in one of the two frames involving the difference and pixelinformation of a corresponding pixel in the other one of the two framesinvolving the difference.
 4. The method of claim 3, wherein the firstdifference set further comprises a difference between pixel informationof the target pixel and pixel information of a corresponding pixel inthe other one of the two frames involving the difference.
 5. The methodof claim 2, wherein the two frames involving each difference in thefirst difference set comprises the current frame, and a frame, which istwo frames prior to the current frame.
 6. The method of claim 2, whereinthe two frames involving each difference in the first difference setcomprises a frame, which is one frame prior to the current frame, and aframe, which is three frames prior to the current frame.
 7. The methodof claim 2, wherein the first criterion comprises a comparison between adifference in the first difference set and a first threshold value. 8.The method of claim 2, further comprising: obtaining a second differenceset between pixel information of one of the plurality of frames andpixel information of another one of the plurality of frames, wherein thetwo frames involving the second difference set are adjacent to eachother; and examining a second criterion with the second difference set;wherein the set of stationary image judgment information furthercomprising the result of a second criterion examination.
 9. The methodof claim 8, wherein the second difference set comprises a differencebetween pixel information of a target pixel in one of the two framesinvolving the second difference set and pixel information of acorresponding pixel in the other one of the two frames involving thesecond difference set.
 10. The method of claim 9, wherein the seconddifference set comprises a plurality of absolute differences, eachdifference being between pixel information of one of a plurality ofpixels within a vicinity of the target pixel and pixel information of acorresponding pixel in the other one of the two frames involving thesecond difference set.
 11. The method of claim 8, wherein the secondcriterion comprises a comparison between a difference in the seconddifference set and a second threshold value.
 12. The method of claim 2,further comprising: obtaining a third difference set among pixelinformation of three successive frames of the plurality of frames; andexamining a third criterion with the third difference set; wherein theset of stationary image judgment information further comprising theresult of a third criterion examination.
 13. The method of claim 12,wherein the three successive frames involving the third difference setcomprises the current frame, a frame, which is one frame prior to thecurrent frame, and a frame, which is two frames prior to the currentframe.
 14. A method for processing an image in a video data, the videodata comprising a plurality of frames, the method comprising: obtaininga first difference set between pixel information of one of the framesand pixel information of another one of the frames, wherein the twoframes involving the first difference set are one frame apart, and thefirst difference set comprises a plurality of differences, eachdifference of the plurality of differences being between pixelinformation of a pixel in one of the two frames involving the firstdifference set and pixel information of a corresponding pixel in theother one of the two frames involving the first difference set; summingabsolute values of each difference in the plurality of differences ofthe first difference set to thereby obtain a sum of absolutedifferences; examining a first criterion according to the sum ofabsolute differences; and performing cross color suppressing operationon pixel information of a current frame of the plurality of framesaccording to a set of stationary image judgment information comprising aresult of the first criterion examination.
 15. The method of claim 14,wherein each difference of the plurality of differences is furtherbetween pixel information of a target pixel in one of the two framesinvolving the first difference set and pixel information of a pixelcorresponding in position to the target pixel in the other one of thetwo frames involving the first difference set.
 16. The method of claim14, wherein the plurality of differences comprises at least onedifference between pixel information of a first pixel in a vicinity of atarget pixel in one of the two frames involving the first difference setand pixel information of a second pixel corresponding in position to thefirst pixel in the other one of the two frames involving the firstdifference set.
 17. The method of claim 14, wherein the first criterioncomprises a comparison between the sum of absolute differences and afirst threshold value.